Electrodeposition of tin



Patented Oct. 5, 1948 ELECTRODEPOSITION OF TIN Elmer F. Harris, Birmingham, Ala", assignor, by i mesne assignments, to Carnegie-Illinois Steel Corporation, a corporation of New Jersey No Drawing. Application October 5, 1945, Serial No. 620,640

'1 Claims. (Cl. 204-54) This invention relates to the electrodeposition of tin and more particularly to anovel method of electrodepositing tin and to an electrolyte by which said method may be carried out.

The invention has among its objects the provision of a novel method of electrodepositing tin, particularly as a coating on products such as strip metal, by which a dense, compact, adherent deposit may be secured under broader ranges of current density, temperature agitation, and other bath conditions than was formerly possible.

Another object of the invention resides in the provision of an electrolyte for the electrodeposition of tin which gives denser and more uniform coatings at high current densities.

These and further objects of the invention will become more fully apparent in the following description. 1

Broadly stated, the invention consists in the addition to acid or neutral electrolytes for tin plating, that is those with a pH value of '7 or less or those having a maximum upper limit in the pH value of 7, an addition agent which broadens the platingconditions, such as temperature of the bath, degree of agitation, and current density, under whichsatisfactory coatings are se cured. The effect of the agent added by the present invention to the plating bath is particularly noticeable in the higher current density ranges, the resulting bath making deposition possible at much higher current densities than formerly could be used. As a result, satisfactory coatings are secured even though plating conditions in the bath are not maintained so accurately as was heretofore necessary.

In the electroplating of continuous strip metal, such as thin strip steel, in connection with which the invention will be described for purposes of illustration, the strip is usually fed continuously to the electrocoating line from coils. In one such practice, the strip after being uncoiled is continuously cleaned and then coated with tin in an electrolytic bath. The coated strip is washed and dried, after which the coating is melted by running the strip through a furnace, to bring the coating to a bright condition and to improve its bond to the base metal. Such procedure is most conveniently carried out with the strip continuously in motion, the leading end of one supply coil of strip metal being joined to the trailing end of an exhausted coil, as by being welded thereto. Such joining of coils end to end, and other conditions whichmay arise in the cleaning, electroplating, and melting line cause at least an occasional variation in speed of the strip through 2 the plating bath. Such variations in speed are compensated for to some extent at least by varying the current density of the depositing current in order to maintain a. substantially uniform thickness of coating metal on the strip. When tin plating electrolytes heretofore known are employed in the coating method above described, however, it has been found that there are certain critical current densities between which the current has to be maintained to insure the deposition of a satisfactory coating. In one such prior electrolyte, the permissible plating range of current density is from to 300 amperes per square foot. Current densities above and below such upper and lower limits, respectively, have been found to yield porous, non-uniform coatings which, even after the melting step, were not so satisfactory as could be desired.

In the practice of the present invention there is added to acid or neutral tin electrodepositing electrolytes a relatively small quantity of diphenyl-para phenylene-diamine, which has the chemical formula CsHrCeHr-CsHMNHz): or structurally Specifically, such added material may range in quantities from .02 to 50 Parts by weight of the, pure material per million of the electrolyte. The addition of diphenyl paraphenylene diamine broadens the current density range which may be used to obtain a satisfactory coating so that electrolytes in accordance withthe description to follow may be satisfactorily operated through current density ranges as high as 600 amperes per square foot. Diphenyl-para-phenylene-diamine does not appear to affect the lower current density range; thus one modification of the electrolyte of the present invention has a current density range of from 140 to 600 amperes per square foot of the material to be plated in the electrolyte, and another has a permissible current density range of 20 to 600 amperes per square foot.

The term diphenyl-para-phenylene-diamine" as employed in this specification and the appended claims refers to the commercial material having the formula CeHs-CsHrCsI-Ia (NH2)2. The quantities stated in each instancein the specification and claims are in terms of parts by'weight of the pure material.

As is disclosed in the copending application Serial No, 620,639, filed of even date, now Patent found to broaden the permissible current density range in its lower portion. When the two such addition agents, that is, diphenyl-para-phenylene-diamine and monobutyl phenylphenol sodium monosulphonate, are employed in an electhere is given theiollowing:

. Example I 'lin (Sn++) grams per liter-.. -60 Phenolsulphonic acid (ortho, meta or para) do 35-110 Dihydroxy diphenyl sulphone- ..do.. 1-9

Diphenyl para phenylene diamine parts per million by weight .02-50 Although electrolytes within the above ranges of components give satisfactory results, it is generally preferred to restrict the components to somewhat narrower ranges which are given in the following Example 11:

Example II Tin (Sn++) grams per liter 28-37 Phenol sulphonic acid (ortho, meta or para) do 65-90 Dihydroxy diphenyl sulphone -..-do 4-65; 49

Diphenyl para phenylene diamine parts per million by weight; .02-50 specified. By the use of the above electrolytes not only is satisfactory deposition under less critical-conditions of temperature and agitation possible, but as above disclosed, the current density range on the upper side is broadened to as high as 600 amperes per square foot. As a further result the diphenyl-para-phenylene-diamine has been found to promote a brighter and better deposit by increasingthe compactness of deposit at all usable current densities, to reduce the tendency for treeing and looseness of deposit at high current densities, and to reduce the tendency oi the surface of the electroplated deposit to oxidize before it is melted.-

I'he dihydroxy diphenyl sulphone ordinarily employed is the reaction product of phenol and sulphuric acid andconsists principally of 4-4 dihvdroxy diphenyl sulphone and 4-2 dihydroxy diphenyl sulphone. For convenience this material is sometimes referred to as phenol sulphone.

Although in the electrolytes set out in the above other acids singly or together. Typical of such other acids are sulphuric acid, fluosiiicic acid, benzene sulphonic acid, cresol-sulphonic acid chlorobenzene sulphonic acid and nitrobenzene sulphonic acid. All of such acids readily dissolve tin from the anodes, and are cheap and easily obtainable. The sulphonic acids are particularly suitable, however, because they form extremely soluble salts of tin. When acids other than phenol sulphonic are employed, the quantities are calculated on the basis of the weight of the acid molecularly equivalent to the range stated for phenol sulphonic acid.

Furthermore, although the electrolyte in the above examples contain phenol sulphone, it is to be understood that other soluble aromatic sulphones may also be used, such as the sulphones oi cresol, resorcinol, and naphthol.

As above indicated, diphenyl-paraphenylenediamine may be employed in electrolytes containing another or other addition agents useful in broadening the lower current density range where the diphenyl-para-phenylene-diamine is not materially adversely eifected by the presence of such other addition agent in the electrolyte. Typical of such other addition agent for broadening the lower limit of the current density range is monobutyl phenylphenol sodium monosulphonate. A typical electrolyte containing both monobutyl phenylphenol sodium monosulphonate and diphenyl-para-phenylene-diamine is given in the following Example III:

Example III Tin (Su grams per liter" 28-37 Phenol sulphonic acid (ortho, meta or para) grams per liter 65-90 Dihydroxy diphenyl sulphone ..do 445 Monobutyl phenyphenol sodium monosulphonate "parts per million by weight" 5-2000 Diphenyl-para-phenylene diamine parts per million by weight" .0240

The addition of the monobutyl phenylphenol sodium monosulphonate broadens the current density range on the lower side to as low as 20 amperes er square foot and thus satisfactory plating may be obtained by use of the electrolyte in Example Ill of from 20 to 600 amperes per square foot. Electrolytes comprising monobutyl phenylphenol sodium monosulphonate as an addition agent, and methods or electrodeposition with such electrolytes, are the subject matter of application Serial No. 620,639 above referred to.

Having thus fully disclosed my invention in connection with the novel method of electrodepexamples phenol suiphonic acid is employed, the

osition and preferred examples of electrolytes for use therein, I desire to claim as new the following.

I claim:

1. An electrolyte for deposition of tin consisting of an aqueous solution of 10 to 60 grams per liter of tiii, an acid of the group consisting, of phenol sulphonic acid, sulphuric acid, fluosilicic acid, benzene sulphonic acid, cresol sulphonic acid, chlorobenzene sulphonic acid, and nitrobenzene sulphonlc acid, the range of acid being 35 to grams per liter for phenol sulphonic acid and the molecular equivalent for the other acids, 1 to 9 grams per liter of dihydroxy diphenyl sulphone, and 0.02 to 50 parts per million by weight of diphenyl-para-p'henylene-diamine.

2. An electrolyte for deposition of tin consisting of an aqueous solution, havinga maximum upper limit in the pH value of 'I, of- 10 to 60 grams per liter of tin, 1 to 9 grams .per liter of a sulphone of a. substance of the group comisting of phenol, cresol, resorcinol, and naphthol, and 0.02 to 50 parts per million by weight of diphenyl-paraphenylene-diamine.

3. An electrolyte for deposition of tin which consists of an aqueous solution of the following ingredients:

Tin "grams per liter 10-60 Phenol sulphonic acid .do 35-110 Dihydroxy diphenvl sulphone do 1-9 Diphenyl-para-phenylene-diamine parts per million by weight 0.02-50 4. An electrolyte for deposition of tin which consists of an aqueous solution of the following ingredients:

Tin "grams per liter" 28-37 Phenol sulphonic acid do 65-90 Dihydroxy diphenyl sulphone 'do-.. 46V Diphenyl-para-phenylene-diamine parts per million by weight... 0.02-50 s. Aneieotmiyte for deposition f tin which v 6 consists of an aqueous solution of the following ingredients: Tin "grams per liter 28-37 Phenol sulphonic acid do 6&90 Dihydroxy diphenyl sulphone do 445 /2 Monobutyl phenylpheonl sodium monosulphonate -parts .per million by weight 5-2000 Diplienyl-para-phenylene-diamine parts per million by weight" 0.02-50 '7. An electrolyte for deposition of tin consisting of an aqueous solution of 10 to 60 grams per liter of tin in the form of a soluble tin salt, 1 to 9 grams 'per liter of dihydroxy diphenyl sulphonic,

and 0.02 to 50 parts per million by weight of diphenyl-para-phenylene-diamine, the maximum upper limit in the pH value of the electrolyte being '7.

ELMER F. HARRIS.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED s'm'ms PATENTS Number Name Date 2,195,409 Flett Apr. 2, 1940 2,271,209 9 Schlotter Jan. 27, 1942 2,313,371 Stack Mar. 9, 1943 l OTHER REFERENCES Transactions of the Electrochemical Society, V01. 80, pp. 391 and 392 (1941). e 

